Balloons are routinely used to resolve or address flow restrictions or perhaps even complete blockages in tubular areas of the body, such as arteries or veins. In many clinical situations, the restrictions are caused by hard solids, such as calcified plaque, and require the use of high pressures to compact such blockages. Commercially available balloons employ complex technology to achieve high pressure requirements without sacrificing the profile of the balloon. Besides high pressure requirements, the balloons should also be resistant to puncture, easy to track and push, and present a low profile, especially when used for angioplasty.
In clinical practice, angioplasty balloons are expanded from a deflated, folded state to an expanded state within a vessel to treat a target area, such as a portion of the circumferential inner wall I of a blood vessel V, as shown in FIGS. 1 and 2. The inflation of a balloon 12 with wall 28 is traditionally completed using an X-ray contrast agent CM along dimension DX to provide better visibility under X-ray or other form of radiography R during the interventional procedure, as illustrated in FIGS. 3 and 3a (which shows the intensity measured by a fluoroscope detector plate, FDP). Typically, a 70/30 percent mixture of contrast agent and saline is used to inflate the balloon during an angioplasty procedure.
In general, a desirable goal is to reduce inflation and deflation times required for balloons without sacrificing the profile of the balloons, especially for large volume balloons (which can require up to two minutes of inflation/deflation times with the contrast agent). Because of its relatively high viscosity, it would also be desirable to eliminate, or at least reduce the amount of, the contrast agent used in inflation/deflation of the balloons. The use of contrast agent prolongs the inflation/deflation times and also poses the risk of iodine exposure to patients sensitive to iodine. In this regard, a non-radiopaque substance could be used in lieu of the contrast agent, such as for example saline or carbon dioxide, but such substances are invisible during X-ray imaging, and thus do not enhance visibility.
Furthermore, the physician performing the angioplasty procedure should be able to locate the position of the uninflated balloon with accuracy, so that the balloon will be properly positioned once inflated. This is conventionally accomplished by attaching marker bands on the catheter shaft in the region corresponding to the balloon working surface. This “working surface” is the surface along the portion of the balloon that is used to achieve the desired treatment effect, such as contacting the calcified plaque (which surface in the case of a balloon having conical or tapering portions at the proximal and distal ends is typically co-extensive with a generally cylindrical barrel section).
Misalignment of the marker bands during placement along the shaft sometimes results in their failure to correspond precisely to the extent of the working surface, as is shown in FIG. 4 (note misalignment amount X between each interior marker band M carried by shaft S and working surface W of balloon 12, which also typically includes a radiopaque tip P at the distal end). Even upon exercising great care to position the markers properly on the underlying shaft in alignment with anticipated boundaries of the working surface when the balloon is inflated, there remains a tendency for mismatch due to several possible factors. One such factor may be the tolerance stack-ups arising as a consequence of the affixation of the balloon to the distal end of the catheter shaft. The balloon also has a tendency to grow in the longitudinal direction when inflated, especially with large and particularly long balloons. Another factor is the tendency of the portion of the catheter shaft within the balloon to bend or flex during inflation. This may lead to misalignment between radiopaque markers fixed to the shaft and the working surface.
Whatever the cause, the resulting misalignment may prevent the clinician from accurately identifying the location of the working surface of the balloon during an interventional procedure. This may lead to a geographic misplacement, or “miss,” of the intended contact between the target area T and the working surface W of the balloon 12 (see FIG. 2). It is especially desirable to avoid such an outcome when the balloon is designed to deliver a payload (such as a drug, stent, or both) or a working element to a specified location within the vasculature, since a miss may prolong the procedure (such as, for example, by requiring redeployment of the balloon 12 or the use of another balloon catheter in the case of a drug coated balloon).
Upon deflation, the balloon may also be subject to a phenomenon known as “pancaking.” In this condition, the balloon 12 folds down upon itself to a flattened state, as shown in FIG. 5. This situation may cause the balloon to be viewed through fluoroscopy as perhaps still being in the inflated condition, since the full width of the balloon may be perceived in the flattened state. This can give the clinician the false perception that the balloon remains inflated, when in fact it is not.
Accordingly, the need is identified for a balloon for which the working surface may be identified during an interventional procedure with enhanced precision. The solution would take into account the possible mismatch between fixed locations on the catheter shaft and the balloon to define the working surface, and would operate independent of the position of the portion of the catheter shaft within the balloon. The improved identification may also allow for the better detection of the false perception of deflation caused by pancaking. Overall, procedural efficiency would be enhanced without remarkably increasing cost or complexity, and in a manner that can be applied to many existing catheter technologies without extensive modification.